Question: Explain the concept of the Observer design pattern.

Answer: The Observer pattern defines a one-to-many dependency between objects, where if one object changes its state, all its dependents are notified and updated automatically.

Example:

class Subject { 
private $observers = []; 
public function addObserver(Observer $observer) { 
$this->observers[] = $observer; } 
public function notifyObservers() { 
foreach ($this->observers as $observer) { $observer->update(); } } }

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